February 15, 2019

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Respiration Responses of Roots, Mycorrhizal Fungi and Free-living Microbes to an Extreme Drought Cycle

Resistance and resilience of auto- and heterotrophic respiration during drought.

The Science

A key uncertainty in models is the impact of droughts on the different sources of belowground respiration, which vary by root traits and mycorrhizal associations. Soil respiration rates of roots, root-associated symbiotic fungi and free-living soil microbes were measured during a drought cycle. To separate the contributions of these three different components of soil respiration, scientists at Oak Ridge National Laboratory grew plants in a greenhouse in specialized pots with mesh partitions during a drought-rewetting experiment.

The Impact

As climate shifts can lead to more extreme droughts, predictive capacity of ecosystem models must be tested with relevant data. This study provides novel insights to the resistance and resilience of roots, root-associated symbiotic fungi and free-living soil microbes, indicating differential rates of decline in respiration during drought and differential legacy effects following rehydration.

Summary

The researchers imposed a drought-rewetting event on mesocosms planted with maple (Acer saccharum Marshall; arbuscular mycorrhizal fungi host) or oak (Quercus alba L.; ectomycorrhizal fungi host) saplings that were separated into heterotrophic or autotrophic compartments. In maple mesocosms, respiration from the root exclusion (hyphae+microbes only) chamber was the most drought resistant, while in oak mesocosms respiration from the microbes only chamber was the most drought-sensitive. Respiration did not recover after rewatering, indicating a persistent drought legacy. In contrast, carbon degrading microbial enzyme activity returned to control functioning after 2 weeks of well-watered conditions. Their results suggest that belowground biota differ in their sensitivity to and recovery from drought, which affects the carbon processes differently. An improved ability to partition carbon fluxes into biotic sources can help to constrain predicted carbon fluxes under future climate scenarios.

Principal Investigator

Jeffrey Warren
Oak Ridge National Laboratory
warrenjm@ornl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

DOE Office of Science, Office of Biological and Environmental Research, Office of Workforce Development for Teachers and Scientists and Office of Science Graduate Student Research (SCGSR) program

References

Ficken, C. D. and J. M. Warren. "The carbon economy of drought: comparing respiration responses of roots, mycorrhizal fungi, and free-living microbes to an extreme dry-rewet cycle". Plant & Soil 435 407–422  (2019). https://doi.org/10.1007/s11104-018-03900-2.